Pb-free Sn/3.5Ag wafer-bumping process and UBM (under bump metallurgy) study

This paper describes newly defined eutectic SnAg solder bumping process using an alloy electroplating method and the interface reactions between four different types of UBM (under bump metallurgy) layers and eutectic SnAg bumps. In addition, the bumping process and UBM reactions of eutectic SnAg were compared with those of eutectic PbSn which is most commonly used as a solder bumping material.